We propose studies to continue insect sting allergy research at Mayo Clinic, the unique feature of which is the use of deliverate insect sting challenges to document the clinical relevance or irrelevance of serological and skin test data obtained from treated or untreated sting-sensitive patients. The specific aims of the project are to 1) investigate the immunological, biochemical, and physiological aspects of insect allergy; 2) determine the frequency of unrecognized (latent) insect sting allergy in the general population; and 3) determine the clinical and immunological response to insect stings in patients who have discontinued venom immunotherapy. We and other investigators have found an inconsistent relationship between the clinical response of sting-sensitive patients to deliberate sting challenge and the in vivo or in vitro measurement of immune reactivity to venom (e.g., skin test results; specific IgE and IgG antibody levels). We postulate that some systemic reactions following insect stings occur via non-EgE-mediated mechanisms, such as: a) delivery of exogenous histamine or histamine-releasing factors in the venom itself; b) release of endogenous histamine by the anaphylatoxins C3a or C5a; or, c) a lowered end-organ threshold to "physiological" quantities of histamine delivered and/or released following stings. These hypotheses will be tested in sting-sensitive patients by: a) determining the skin test endpoint to insect venoms, codeine, anti-IgE, and histamine itself; b) measuring the physiological response to graded intravenous infusions of histamine; and, c) measuring the plasma levels of histamine and other mediators following deliberate insect sting challenge. To determine the frequency of unrecognized (latent) sting sensitivity in the general population, we will screen healthy volunteers using venom skin tests and healthy blood bank donors using measurements of venom-specific IgE antibodies. The clinical relevance of positive test reactions will be determined by subsequent deliberate insect sting challenges. Likewise, we will study in the same fashion formerly sting-sensitive patient who have discontinued venom immunotherapy, to determine if there is a minimal or optimal duration for venom immunotherapy. If successful, these studies should provide more information on the pathophysiological events occurring during insect sting reactions and provide more definitive guidelines for institution and/or continuation of venom immunotherapy programs.